Radiofrequency (RF) devices are used to ablate or heat different types of tissue. For example, in the field of dermatology RF devices are used to treat aging skin. Skin aging is associated with changes in the upper levels of the skin such as roughness of the skin due to changes in the stratum corneum and epidermis and uneven pigmentation in the epidermis. In the dermis, aging and environmental factors cause the destruction and malfunction of collagen and elastin fibers leading to the formation of wrinkles. Symptoms of skin aging in the epidermis are typically treated by ablative methods such as chemical peels or laser resurfacing. Optical radiation devices such as lasers are used to resurface large areas of the skin. While these lasers are effective in the treatment of the signs of skin aging, resurfacing the whole epidermis is often associated with side effects such as wound infections, prolonged healing times, hyperpigmentation, hypopigmentation, and scarring.
Radiofrequency devices are used to ablate localized skin lesions or to destroy the whole upper surface of the skin. However, whole skin resurfacing methods and devices cause burn-like post treatment reactions that may be associated with prolonged healing times, increased risk of infections, prolonged erythema, scarring, hyperpigmentation, and hypopigmentation.
U.S. Pat. No. 6,711,435 discloses a device for ablating the stratum corneum epidermis of a subject, including a plurality of electrodes, which are applied to the subject's skin at respective points. However, this device does not ablate the epidermis or dermis and thus has no effects on the signs of skin aging.
Symptoms of skin aging in the dermis are typically treated by non-ablative methods, including lasers, intense pulsed light, or RF devices that heat the dermis to trigger renewal of collagen fibers. In order to trigger collagen renewal, some RF devices use bipolar electrodes to increase the heat of dermal skin layers through the creation of electrical currents that flow parallel to the skin surface. These devices use active and return electrodes that are typically positioned relatively close to one another at the treatment site. In some cases, the two electrodes are located on the same electrosurgical probe, and the electrodes alternate between functioning as active and return electrodes. Typically, for bipolar devices, electrical currents created in the target tissue create a density gradient in which the upper layers of tissue (i.e., those layers of tissue nearer to the electrodes) carry more current, while the lower layers of tissue (i.e., those layers of tissue farther from the electrodes) carry less current. Therefore, electrical current density varies inversely as a function of depth below the surface of the tissue being treated. Other RF devices use unipolar or monopolar electrical energy for heating the deep layers of skin. These devices also use an active electrode and a return electrode. The return electrode is typically positioned a relatively large distance from the active electrode (in comparison with bipolar devices). For both unipolar and bipolar devices, current flows along the lowest impedance path between electrodes.
The devices described previously lack the ability to control the spatial directions, energies, and/or nature of the electrical energies affecting the treated area and thus lack the selectivity and specificity needed for maximum efficacy in their respective therapeutic indications. Moreover, the non-ablative bipolar and monopolar RF devices lack the ability to treat the signs of aging in the epidermis. Enhanced ability to control the spatial directions and the pattern of electron flows in the treated biological tissue would allow effective therapy for additional dermatological and non-dermatological disorders such as hair removal, acne, acne scars, cellulite, psoriasis, bone grafting and more.
Despite advancements in the use of RF devices for treating biological tissue, therefore, there continues to be a need in the art to develop effective ablative and non-ablative electrosurgical devices and methods that are suitable for treating a wide variety of conditions. An ideal electrosurgical method and related devices would be capable of selectively and specifically treating a wide variety of biological tissues and conditions affecting such tissues. Such a method and the associated devices would be simple to use, and would have minimal adverse effects.